传动轴结构损伤识别的数值模拟试验

在带有裂纹的轴结构件中,当裂纹较小时,传动轴的裂纹参数与其固有频率的变化率相关联。通过对由固有频率的变化率确定轴结构件裂纹参数的理论分析和通过截取频率变化率趋势图的等高线并取其交点来反推出裂纹的位置和深度的方法,可识别其裂纹位置和深度。文中给出了有关计算公式,并进行了数值模拟。从模拟结果看,这种方法可以很好地识别传动轴的损伤程度,从而为轴结构件的改进设计及含裂纹的轴结构件剩余寿命的估算提供了理论依据。     

梁类结构多裂纹微弱损伤的小波有限元定量检测方法

提出了一种定量检测梁类结构多裂纹参数的方法。利用适宜求解奇异性问题的小波有限元法,从动力学正问题入手,对裂纹梁进行有限元建模,获得裂纹故障在结构固有频率上反映的本质征兆,并利用曲面拟合技术绘制出以裂纹位置和深度作为变量的固有频率变化率曲面,然后对整个裂纹梁进行剖分,迭代求解出每个剖分单元上的结构损伤系数。损伤系数为正的单元诊断为裂纹单元,在每个裂纹单元上求出裂纹对应的前三阶固有频率变化率,并分别将其作为输入参数代入固有频率变化率曲面,做出前三阶模态的频率变化率等高线,最后通过三条等高线的交点预测出裂纹存在的位置和深度,算例分析验证了该算法的有效性。     

含有裂纹的齿轮轴动力特性分析与模拟

将裂纹梁理论应用于齿轮轴的动力学研究当中，以轴开放裂纹作为研究对象，对齿轮轴出现裂纹后的动力特性进行了分析模拟，并对裂纹位置和裂纹尺寸等对轴特性的影响进行了深入探讨，指出裂纹发生位置对齿轮轴的振型有着直接的影响，在裂纹发生处振型发生突变，而裂纹尺寸对轴的振型和固有频率都有影响，当出现裂纹后齿轮轴的固有频率发生下降，越是大尺寸的裂纹，轴固有频率越是下落显著。这对齿轮轴的损伤监测和诊断具有重要价值。     

基于固有频率变化的两焊点接头的疲劳损伤参量

使用有限元软件ABAQUS分析两焊点拉剪试样在疲劳裂纹扩展过程中的动态响应,研究固有频率随裂纹面积的变化.将裂纹截面积作为损伤面积,确定损伤与固有频率变化率的关系.利用损伤力学中损伤随寿命的演化规律,对疲劳损伤达到一定程度的试样进行疲劳寿命预测.结果表明,此损伤参量能较好地描述双焊点结构的疲劳破坏过程.     

基于小波有限元技术的单螺杆压缩机螺杆轴的裂纹识别

为了能够有效地对单螺杆压缩机螺杆轴进行裂纹识别,以小波有限元技术为支撑,提出了单螺杆压缩机螺杆轴的裂纹识别方法.首先,结合有限元理论和Daubechies小波提出了适用于单螺杆压缩机螺杆轴裂纹识别的小波有限单元;然后,建立了单螺杆压缩机螺杆轴的振动小波有限元方程,可以对含有不同裂纹的螺杆轴进行固有频率的计算;接着,生成了裂纹识别数据库;最后,通过对4种含有不同裂纹的螺杆轴进行裂纹识别,验证了该方法的有效性.     

基于小波变换的轴力杆裂纹识别

基于裂纹识别中的正反问题,以裂纹轴力杆为例,将有限元与断裂力学相结合,建立了裂纹轴力杆动力学模型,推导了裂纹轴力杆单元等效刚度矩阵,求解出不同裂纹位置和尺寸下系统固有频率;利用小波变换对采集的故障信号进行小波分解和谱分析,使得故障信号的频率在小波分析的细节信号中得到放大,对比该频率和各种故障下计算的故障频率理论值确定裂纹相对位置和尺寸。算例证实了该算法的有效性,为工程结构轴力杆裂纹故障诊断提供了新方法。     

挖掘机斗杆轴座焊缝裂纹产生的原因及控制措施

<正>1.故障现象随着自动化技术的发展,挖掘机斗杆逐步由机器人焊接代替手工焊接。某型号挖掘机斗杆在使用焊接机器人焊接(MAG焊)后,在斗杆Ⅱ轴轴座环状焊缝出现裂纹,如图1所示。斗杆是挖掘机的关键结构件之一,在作业过程中承受交变载荷。本文分析斗杆Ⅱ轴轴座环状焊缝裂纹产生的原因,并提出控制措施。     

基于层次分析法的港口起重机结构件安全评价

针对在役港口起重机结构件出现裂纹缺陷后的安全评价问题,文中以裂纹、强度、刚度、变形和锈蚀等作为安全评价指标,建立了基于层次分析法港口起重机带裂纹结构件的安全评价体系,基于结构件现场实测的数值,实现对港口起重机带裂纹结构件的安全评价。     

应用有限单元法的机床进给系统轴扭特性分析

基于有限元法建立了考虑轴扭耦合的机床进给系统动力学方程,分析了工作台位置变化对其动态性能的影响.结果 表明:第1、3阶固有频率为丝杠和工作台的轴向振动模态,第2阶为丝杠扭转振动模态.随着工作台位置变化,第1阶固有频率呈现先减后增的变化,最大值出现在丝杠端部,变化率达50.58％;第3阶固有频率为先增后减的变化规律,其中最大值出现在丝杠中部,变化率为10.3％;试验结果与计算结果相吻合;第2阶固有频率受工作台位置变化影响不大,验证试验结果与仿真结果相一致,证明这里的进给系统动力学模型具有较高的精度.     

基于ANSYS Workbench的六轴机械手焊缝打磨的有限元分析

某企业采用ABB六轴机械手实现恒力、恒行程打磨结构件焊缝,因打磨过程中振动较大,需避开设备的固有频率,还需对打磨过程中引起的受迫振动进行分析.因此,采用SolidWorks对六轴工业机械手进行建模,利用ANSYS Workbench软件对其模态振型和谐响应特性进行分析,得到了模态振型数据和简谐响应曲线,仿真检验了该工业...     

受弯梁中开裂纹的位置识别与分析

利用有限元计算判定受弯梁中开裂纹的位置 ,从中得出 :同正常梁相比 ,裂纹梁的固有频率与振型的变化不但与裂纹深度而且与裂纹位置有关 ,因而 ,通过裂纹梁低阶固有频率及振型的变化情况可以判定裂纹的位置。对于裂纹较浅的情况 ,直接利用振型与固有频率的变化很难判定裂纹的位置 ,必须借用一些特征参数来提高识别的敏感性 ,这样 ,裂纹梁中早期裂纹的识别也是可行的     

Detection and localisation of multiple cracks in a shaft system: An experimental investigation

Experimental verification of an algorithm for detection and localisation of multiple cracks in a simple shaft system is presented. Cracks in a shaft cause the slope discontinuity in the shaft elastic line. The algorithm is based upon detecting the slope discontinuity due to cracks. Two simply supported non-rotating shafts are used for the experimentation. Both the shafts are tested with single as well as double artificially introduced open cracks. Transverse deflections of the shaft due to sine-sweep excitation force through an exciter are measured at regular axial locations of the shaft. The slope discontinuity is obtained by fitting shaft deflections at regular axial locations in a quadratic polynomial. The algorithm uses shaft deflections at several excitation frequencies to incorporate adequate modal information in the response to improve the crack identification. A scheme is proposed to improve the working of the algorithm in low signal to noise ratio conditions. The algorithm identifies the presence of crack and successfully locates the crack along the shaft length.     

裂纹耦合双转子响应的非线性时间序列分析

建立了裂纹耦合双转子系统的动力学方程,分析了含有裂纹、支承在挤压油膜阻尼器上耦合双转子的复杂运动。采用非线性时间序列方法,对不同裂纹时系统的响应进行分析,估算了其最大Lyapunov指数和关联维数。结果表明,裂纹使轴的刚度下降到一定程度后,其响应由拟周期到周期运动,最后失稳。关联维数和Lyapunov指数相结合能为判断因裂纹变化引起的系统运动状态改变提供一种辅助方法。     

Crack detection, localization and estimation of the depth in a turbo rotor

The goal of this paper is to describe an advanced method of a crack detection: a new way to localize position and to estimate depth of a crack on rotating shaft. As a first step, the shaft is physically modelled with a finite element method and the dynamic mathematical model is derived using the Hamilton principle; thus, the system is represented by various subsystems. The equations of motion of the shaft with a crack are established by adapting the local stiffness change through breathing and gaping from the crack to an undamaged shaft. This is the reference system for the given system. Based on a model for transient behavior induced from vibration measured at the bearings, a nonlinear state observer is designed to detect cracks on the shaft. This is the elementary NL-observer (Beo). Using the observer, an Estimator (Observer Bank) is established and arranged at the certain position on the shaft. When a crack position is localized, the procedure for estimating of the depth is engaged.     

裂纹条件下轴类锻件锻造中温度场分析模型

基于非稳态热传导理论建立了对称与非对称裂纹条件下轴类锻件的二维温度场分析模型。该模型结合复合介质理论,首先运用集总参数法求解对称裂纹锻件的裂纹介质温度场,得出裂纹对应的温度场函数,然后将其作为对称裂纹条件下轴类锻件热传导方程的边界条件,通过求解热传导方程得到对称裂纹条件下轴类锻件的温度场分析模型;其次,通过引入修正系数得到非对称裂纹的温度场函数,将该温度场函数作为非对称裂纹条件下轴类锻件热传导方程的边界条件,求解热传导方程得到非对称裂纹条件下轴类锻件的温度场分析模型。实验验证了该模型的可行性。     

简支梁中裂纹参数的识别

结构中的裂纹对系统振动特性将产生一定的影响 ,一般来讲 ,裂纹参数与振动特性的改变之间很难有直接的函数关系 ,通过振动参数的改变来识别裂纹有一定的困难 ,本文经过计算证明 :对于受弯的两端简支梁 ,当裂纹较小时 ,梁的自振频率的变化率与裂纹参数之间存在明确的函数关系 ,利用这一函数关系 ,梁中的裂纹深度与裂纹位置可由自振频率的变化率计算得出。同时证明 :对于简支梁而言 ,单纯利用自振频率无法唯一地确定裂纹位置 ,只能唯一地确定裂纹的深度     

The dynamic behavior of a rotor system with a slant crack on the shaft

For a Jeffcott rotor system with a 45° slant crack on the shaft, the motion equations are established with four directions, i.e. two transversal directions, one torsional direction and one longitudinal direction. It can be seen from the deducing process of the stiffness with the strain energy release approach that there are coupling stiffnesses of bending–torsion, bending–tension and torsion–tension for the slant-cracked shaft and only bending–tension for the transverse-cracked one. The paper shows that besides the coupling stiffnesses, there is bending–torsion coupling caused by the eccentricity. All these couplings affect the responses of the slant-cracked shaft and the transverse-cracked one. Comparing responses of a cracked shaft with an open crack model and those with a breathing crack model finds that there are the same prominent characteristic frequencies for these two kinds of shafts, even though the cracked shaft with a breathing crack model behaves much more non-linear than that with an open crack model. Therefore, almost all studies in this paper adopt the open crack model since it needs taking much longer time to compute responses of a breathing cracked shaft than that of an open cracked shaft. Analyses of steady responses indicate that the combined frequencies of the rotating speed and the torsional excitation in the transversal response and the frequency of the torsional excitation in the longitudinal response can be used to detect the slant crack on the shaft of the rotor system.     

梁结构裂纹参数的识别方法

以Bernoulli-Euler梁振动理论为基础,引入断裂力学中能量释放率的概念,得到承弯梁出现横向裂纹时其固有频率的变化与裂纹参数的简化表达式,讨论梁裂纹参数、几何参数对固有频率的影响。利用这一表达式,提出一种识别裂纹位置和深度的数值方法,最后,用含裂纹等截面悬臂梁的实验验证所提方法。结果表明,在固有频率误差较小的情况下,文中方法可给出梁结构中裂纹位置和深度,可为更精确的局部探伤指出探测范围。     

On multiple crack detection in beam structures

This study presents an inverse procedure to identify multiple cracks in beams using an evolutionary algorithm. By considering the crack detection procedure as an optimization problem, an objective function can be constructed based on the change of the eigenfrequencies and some strain energy parameters. Each crack is modeled by a rotational spring. The changes in natural frequencies due to the presence of the cracks are related to a damage index vector. Then, the bees algorithm, a swarm-based evolutionary optimization technique, is used to optimize the objective function and find the damage index vector, whose positive components show the number and position of the cracks. A second objective function is also optimized to find the crack depths. Several experimental studies on cracked cantilever beams are conducted to ensure the integrity of the proposed method. The results show that the number of cracks as well as their sizes and locations can be predicted well through this method.